In sequential injection, such as when an injection valve that is capable of being individually triggered is allocated to each cylinder, fuel usually is injected in a way that permits the actual total quantity of fuel required at any one time (total fuel quantity) to be ejected before the intake-valve arrangement opens for the particular cylinder. However, this causes condensation of fuel on the corresponding suction pipe and, thus, leads to a so-called wall film. In steady-state processes, this wall film does not have a disturbing effect. However, in non-steady processes, the wall film creates errors in the metering of fuel into a cylinder because fuel which should be available for combustion is either stored in the wall film or released from the wall film. Accordingly, the aspirated air is enriched with fuel to a greater degree than actually desired. To avoid these disadvantages, in a method described by German Printed Patent No. 36 09 798, the fuel is not stored in advance (i.e., is not ejected before the intake-valve arrangement opens), but rather is ejected only after it opens.
Other than the above-mentioned processes, in which the total fuel quantity is either completely stored in advance or completely injected into the valve opening, a considerable portion of the total fuel quantity may be injected so that it is stored in advance, with a residual quantity being ejected shortly before the intake-valve arrangement closes. In this manner, a particularly good ignitable mixture is attained in the upper part of the mixture that was aspirated.
Despite these various methods and devices for injecting fuel, the problem still exists with regard to finding a method and device which will allow the injected fuel to evaporate as optimally as possible while largely avoiding the formation of wall film.